1. Field of the Invention
This invention relates to off-shore well-drilling and related equipment and, more particularly, to a prefabricated drilling and production platform; a prefabricated support for the platform; and jacking means for elevating the platform on the support.
2. Description of the Prior Art.
Prefabricated drilling and production platforms and supports therefor, and jacking mechanisms for raising the platforms on the supports have been devised heretofore, but many of these are suitable only for use in shallow and relatively calm waters. Some of such prior platforms have utilized jacking mechanisms including racks and pinions with the racks attached to sauare spuds, but these have the disadvantage that the spuds must be pre-mounted in openings in the platform and the racks indexed with pinions mounted on the barge, so that proper engagement can be effected. Such structure is shown in Bulkley et al., U.S. Pat. No. 2,589,146. Racks and pinions when applied to caissons have the further disadvantage that pressure loads are applied to local areas of the caissons, which may cause damage or collapse, or require excessive and undesirable internal bracing of the caissons. Internal bracing is particularly objectionable when conductor pipes are to be located in the caissons.
Other prior jacking devices include annular rubber tube-like elements carried by the barge or platform and surrounding the caissons. A jack of this type is disclosed in Suderow U.S. Pat. No. 2,948,119. The rubber elements must be inflated by air to grip the caissons, and manipulated to elevate the barge on the caissons. Such devices are objectionable because the rubber elements are subject to rapid wear, blow out, require substantial maintenance and frequent replacement. Furthermore, they have a tendency to slip relative to the caissons, particularly if the exterior surface of the caissons is contaminated by oil, algae, or mud. Such devices are also subject to failure and allowing the barge to drop back onto the water whenever the air supply fails, as by the rupture of an air hose.
Still another jacking device, known as a cable jack includes criss-crossed cables that are operable for positively gripping the exterior of the caissons and raising the platform on the caissons. Such jack is disclosed in my prior U.S. Pat. No. 2,858,105. The cable jacks are much more satisfactory than the rack and pinion type jack, and the inflatable rubber tube device. However, all of the foregoing types of jacking devices take considerable time to "set up" and to be operated to effect elevation of the platform to the desired working height. Such jacking devices are unsuitable for use in rough waters because of the potential damage to either the caissons or the platform, or both, during the period that the platform is subject to movement by wave action. The hazards, of course, are less after the platform has been raised above wave level effect.
A so-called "pin" type jacking system is disclosed in Suderow U.S. Pat. No. 2,932,486. In such system channel members with spaced openings are welded to opposite sides of the caissons, and jacking mechanisms including hydraulically operated pins receivable in said openings are intended to raise a barge relative to the caissons. However, such system presents the problem of aligning the pins with the openings, as well as the possibility of the pins becoming bent and jamming so that retraction is impaired, if not rendered impossible.
A prefabricated platform support structure that is towed to the drilling site and sunk, is not new per se. A structure of this type is disclosed in the patent to Kuss et al., U.S. Pat. No. 2,586,966. However, the patentees contemplate building a platform on the caissons after the support has been anchored to the sea bed. Such procedure is objectionable because it is expensive, slow, impractical, and very hazardous. Considerable auxiliary equipment is required in the way of tugs and lighters to bring the platform components to the site, and derrick barges are required for use in erecting the components on the caissons. Obviously, no erection work can be done in rough seas, at which time all personnel and rented equipment remain idle at tremendous costs.
A prefabricated platform with three caisson wells has heretofore been used with a prefabricated tripod support in constructing a structure known as Texas Tower No. 4. Jacking devices somewhat similar to the type of cable jack disclosed in Nixon U.S. Pat. No. 2,833,188 were employed, but a great deal of time was wasted in threading the cables through the gripping devices before the hoisting operation could be started, and during which "set up" time the platform and caissons were in constant danger of being seriously damaged by wind and wave action. The danger continued during the jacking operation, which was very slow, and until the platform was raised high enough to clear the waves.
The foregoing objections and disadvantages are overcome by the apparatus and methods for quickly erecting off-shore platforms disclosed in my prior U.S. Pat. Nos. 3,876,181 and 4,041,711, over which the present invention constitutes an improvement, particularly with respect to a more stable platform support, and a simplified jacking system, which results in great savings in "set up" time, jacking time and in the tonnage of steel required in fabrication. These factors assure substantial savings in labor and material costs, both of which are important considerations in all off-shore drilling ventures. Moreover, since the present platform and support are prefabricated and equipped prior to installation, the need for derrick barges and other construction equipment is eliminated, together with their extremely high rental costs. Also of prime importance is the safety factor, which is provided by the "fail safe," yet economical, jacking units of the present invention, which automatically prevent dropping of the platform during the jacking up operation.